1. Field of the Invention
This invention relates to a carrier to be used in the preparation of a catalyst for use in the production of ethylene oxide, a catalyst obtained by depositing a silver-containing catalytic component on the carrier and used for the production of ethylene oxide, and a method for the production of ethylene oxide by the use of the catalyst.
2. Description of the Related Art
Concerning the catalyst for use in the production of ethylene oxide by gas phase oxidation of ethylene and the carrier therefor, numerous reports have been heretofore introduced to literature.
JP-A-57-171,435, for example, has a description to the effect that a carrier obtained by adding mullite, colloidal silica, etc. to .alpha.-alumina having a deliberately lowered sodium content has a high specific surface area, a uniform pore distribution, and moreover high wear-resistant properties. EP-B-0,207,550 has a description to the effect that a carrier having a small impurity is obtained by mixing an aluminum compound with the salt of a Group IA metal in the Periodic Table of the Elements and calcining the resultant mixture and a catalyst using this carrier excels in stability. JP-A-04-363,139 discloses a carrier containing .alpha.-alumina the elements of the fourth, fifth, and sixth periods (such as, for example, titanium, tin, and hafnium) of the IIIa--VIIa and IIIb--Vb groups in the Periodic Table of the Elements and contains a description to the effect that a catalyst using this carrier has high selectivity and a long life. Further, U.S. Pat. No. 5,100,859 discloses a carrier comprising high-purity .alpha.-alumina, the oxide of an alkaline earth metal, a silicon oxide, and zirconium oxide and contains a description to the effect that a catalyst using this carrier has high initial selectivity and a long life.
We have also proposed a catalyst obtained by depositing silver and cesium as catalytic components on a carrier having a coating layer of amorphous silica disposed on the surface of .alpha.-alumina and used for the production of ethylene oxide (U.S. Pat. No. 5,077,256) and a catalyst obtained by disposing a coating layer of amorphous silic-alumina on the surface of .alpha.-alumina and depositing silver and cesium as catalytic components on the resultant carrier and used for the production of ethylene oxide (U.S. Pat. No. 5,395,812).
The catalysts which are disclosed in U.S. Pat. No. 5,077,256 and U.S. Pat. No. 5,395,812 are excellent in catalytic performance and are fully satisfactory from the commercial point of view. Ethylene oxide, however, is produced on a large scale. Even such a small addition to selectivity as 1%, therefore, results in a notable saving in ethylene as a raw material. In the light of the prominence of the economic effect of such an improvement in the selectivity, the desirability of developing a catalyst of more improved performance for the production of ethylene oxide has been finding growing recognition.
An object of this invention, therefore, is to provide a carrier to be used in the preparation of a catalyst for the production of ethylene oxide, a catalyst obtained by depositing silver-containing catalytic component on the carrier and used for the production of ethylene oxide, and a method for the production of ethylene oxide by the use of the catalyst.
Another object of this invention is to provide a carrier which permits preparation of a catalyst possessed of excellent catalytic performance in terms of activity, selectivity, a and used for the production of ethylene oxide, a catalyst obtained by using the carrier just described, endowed with excellent catalytic performance, and used for the production of ethylene oxide, and a method for the production of ethylene oxide by the use of the catalyst just described.